Yeah -
This seems to be the order:
1. Most typical basic setup is the single 2-way speaker on each side on stands.
(Stands to keep the horns above the audience's ears)
2.Then adding sub-woofer component, gets added to each side. Includes adding a crossover - more amplifiers (subs need a more powerful amp). Almost always mono on the subs. Many have pole holders that let you put the 2-way mains above them.
3. From there - many permutations exist. Bi-amping the tops, Ganging subs together, 4-way, 5-way systems.... as many choices as you could ever desire.
For advice on speakers - you'll get lots of opinions.
Be very careful not to just get advice from the typical "big-box" musical instrument stores. Not that they are all bad - but I've seen some very bone-headed junk that comes out of them.
I don't endorse any of the following - just because I don't use them - but:
The Yamaha on the low end seem to get some respect here at an advantageous price point.
Yorkville seems to give very good service to a lot of folks in the lounge.
The JBL higher-end music store stuff (SRX/MRX) also gets some kudos.
The biggest problem I hear from the MI store stuff is that while it may seem loud - it just lacks low-end puch, sparkle and mid-range clarity. (Big, dumb, loud, sounds like mush)
I've had good results with EV, QSC amps, ISP Technologies active speakers, EAW and JBL monitors. (I do outdoor festivals to about 2,000 people (rock, blues etc) and indoor shows to about 800 people for hardcore, pop, punk, big band, bluegrass and rockabilly)
As for advice - find someone who does your same musical style and listen to some live gigs for advice - and then compare what you hear to the sound you get at a big professional concert.